Technical Field
The present invention relates generally to wind turbulence sensing, and more particularly, to a system and method for remote wind turbulence sensing using Orbital Angular Momentum (OAM) Light Detection and Ranging (LIDAR).
Description of the Related Art
Recently, aircraft safety is becoming an increasingly important issue in light of accidents and incidents over the past several decades. For example, when flying through the atmosphere, a plane is continually subject to various aerial effects, and an abrupt change in the atmosphere (e.g., wind turbulence) may cause an aircraft to have an incident (e.g., airplane crash). Wind turbulence is a random, chaotic motion of air that can structurally damage the plane and injure its passengers, and may be caused by changes in air currents. Generally, there is at least dust, water droplets, pollution, pollen, and/or salt crystals in the atmosphere. Wind shear is a micro-scale meteorological phenomenon over a relatively small distance in the atmosphere, which may produce severe weather (e.g., tropical cyclone).
These atmospheric conditions (e.g., wind turbulence, wind shear) can pose serious hazards to aerial navigation. Therefore, information of the atmospheric turbulence imposing on free-space communication channels may be significant for optical system design operating in such an environment. If the pilot can have prior knowledge of wind shear, down burst, or clear air turbulence, then airline safety may be improved. For example, the pilot can direct the aircraft in such a manner to evade wind turbulence so that fierce aircraft body movements are reduced. Furthermore, the passengers can be alerted in advance regarding the upcoming wind turbulence by means of a communication to ease conceivable panic.
Conventionally, remotely sensing air turbulence (e.g., wind shear, wind turbulence, etc.) in navigable airspace has been attempted by, for example, using coarse interference filters with wide spectral bandwidth to isolate spectral regions with weak absorption to obtain range information. However, since the coarse interference filters mass many spectral lines and transmit spectral lines of interfering gases, such as water vapor and ozone, whose concentrations were unknown and variable, precise range information could not be obtained.
A tunable Fabry-Perot etalon has been used for remote sensing of wind turbulence, and may include double-pulsed, visible or near-infrared sources, and direct detection. The spatial temperature profile ahead of an aircraft is detected by continually sensing the intensity of the thermal radiation from the column of atmospheric air, and comparing the relative intensity of the spectral peaks over time to achieve wind turbulence prediction. Such devices also require large, cumbersome, expensive transmitters, they are susceptible to interference by smoke, dust and fog as well, and require complex electronic systems to interpret the received signals.
A speckle-turbulence system has also been employed, and may include crossed beams and multiple detectors for achieving wind turbulence remote sensing. The advantage of a speckle-turbulence system is the ability to measure the vector wind in a plane perpendicular to the line of sight, but this also greatly complicates the system. Furthermore, the continuous wave speckle-turbulence system has to use a hard target, such as the earth or a building, so it cannot be operated with an aerosol-like target. In other words, pertaining to some wind shear warning devices mounted ahead of the aircraft, not only is awareness delayed and a warning hastily emitted without prior notice, but it is also impossible to confirm whether this warning is dependable or not using conventional systems and methods.